Radio Frequency (RF) search systems convert RF energy into a stream of time domain data. The RF search systems perform the search function with an antenna, an RF tuner, an Analog-To-Digital (ADC) converter, and computer processing equipment. The ADC represents the RF energy in the time domain. The time domain data is then translated into a frequency domain via a Fast Fourier Transform (FFT). Once in the frequency domain, a threshold is applied to distinguish RF energy from a noise floor.
A detection algorithm is applied to compute the frequency and bandwidth of a Signal of Interest (SOI). The algorithm includes routines to extract additional features of the RF energy, such as its centroid frequency and total power. A system with the characteristics described above using the amplitude of the RF energy to distinguish from the noise floor is termed an “energy detection” system. An example of such an energy detection RF search system is the E3238s from Agilent Technologies, Inc. of Santa Clara, Calif.
A wideband Bearing Finding (BF) system is an enhanced search system using the bearing (direction) properties of the RF signal to characterize the SOI. The wideband BF system can collect multiple RF signals simultaneously. The wideband BF system comprises two or more wideband tuners and digital signal processors to identify the bearing of the RF signals.
FIG. 1 is a block diagram of a wideband BF system 101. An antenna array 103 collects multiple RF signals simultaneously. The wideband data stream 105 is fed into wideband tuners 107 and ADCs 109 before being converted into multiple narrowband streams 113 that are fed to a BF algorithm 111.
The wideband BF system 101 contains energy detection capabilities to improve the energy detection process. The energy detection capability is provided in the form of an energy detection process 115 as an input to the BF system 101. The wideband BF system 101 is tasked to locate and identify an RF signal when first instructed by the energy detection process 115. Once an energy detection is affirmed, the wideband BF system 101 acquires from the BF algorithm 111 the direction for the frequency of the energy detection. The output of system 101 is a list of valid direction detections 117. An example of such a wideband BF system 101 is the Model 803WT VHF/UHF COMINT BF System from TCI of Fremont, Calif.
Antenna directionality can also be employed to increase the probability of locating an SOI in the energy detection RF search system. Unfortunately, a major challenge encountered by the energy detection RF search system described above is the inability to detect low-level signals, and legitimate signals embedded in the noise floor (“noise-like”). Additionally, energy detection RF search systems can be overloaded with additional detections generated from identifying signals from all directions, even when an SOI has been identified beforehand.
In another scenario, an RF signal bordering on the amplitude threshold might not meet the energy detection criteria. The RF signal can be detected if the amplitude threshold were adjusted. A disadvantage of adjusting the threshold is an increase of the total number of energy detections and a decrease in quality of the energy detections. This can be a major issue to systems that receive these detections. These systems must be able to handle the rate of detections that typically lead to larger, heavier, and more power consuming systems. These solutions lead to a higher expense in operating such systems.
The wideband BF system 101 can detect the SOI with greater precision, but inherits the disadvantages of the energy detection. This is because the wideband BF system 101 is tasked by the energy detection 115 input to identify the SOI.
Accordingly, a need exists to accurately search and identify an SOI.